Boiling of water droplet in glass-oil-water multiphase system

Boiling a volatile droplet in non-volatile liquid is complex because of various interface interactions in a solid-liquid-liquid system. Previous studies have reported explosive boiling and attributed this phenomenon to heterogeneous nucleation due to solid-liquid contact. In this study, we investigated the boiling of an approximately 2 mm-diameter water droplet in a silicon oil pool inside a glass container. Two transition temperatures were observed: 122.5 degrees C (for the transition from evaporation to boiling) and 160.0 degrees C (for the transition from the bubble growth on the oil side to that on both the oil and water sides). Moreover, four boiling modes were identified: evaporation (E), boiling in water (BIW: bubble nucleation at the glass-water interface and growth inside a drop), boiling in oil (BIO: bubble nucleation at the oil-water interface and growth in oil), and boiling in oil and water (BIOW: bubble nucleation at the oil-water interface and growth in oil and water). For the first time, boiling bifurcation was observed for drop boiling in a three-phase system. For the oil temperature ((T)b) in the range 122.5-160.0 degrees C, the boiling mode switches between BIW and BIO. In contrast, for T-b exceeding 160.0 degrees C, either BIW or BIOW occurs. This bifurcation occurs because droplets prefer minimum activation energy between that for the bubble nucleation at the solid-water interface and that for the bubble nucleation at the oil-water interface. Interfacial instabilities were analyzed to explain why BIOW was more violent than BIW. This work presents a comprehensive understanding of droplet boiling in a three-phase system.